I. Field of the Invention
The present invention relates to a method and composition for increasing body weight and stimulating the immune systems of domestic animals poultry and fish, and to a feed comprising the same.
II. Description of the Related Art
Immune organs and immunocytes of domestic animals and poultry in infancy do not work very efficiently, so that infant domestic animals and poultry have innate immune disorders. Therefore, they are liable to suffer from infectious diseases which attack the digestive system or the respiratory system, such as scours or diarrhea, representing a serious problem in the livestock industry. For example, the rate of occurrence of scours in infant swine during the lactation period or ablactation period is as high as 40%-100%. The economic loss due to the death or developmental delay in infant swine suffering from diarrhea or white diarrhea is very large, and is a serious problem in the swine raising industry.
For the treatment or prophylaxis of such infectious diseases, various antibiotics and sulfa drugs are used. However, their effects are not always satisfactory and their use is being suppressed because of the problem of residual drugs and the generation of drug-resistant bacteria.
Thus, there is a great demand for a drug which prevents or cures infectious diseases of infant domestic animals and poultry, which is not a bactericide such as an antibiotic.
It was recently found that components separated from cell walls of microorganisms such as BCG(Bacillus Calmette-Guerin) and Norcadia have a stimulating or strengthening effect on the immune system, and that the effective components are peptide glycans ("Journal of National Cancer Institute", vol. 52, p. 1571, 1974; "Gann", vol. 69, p. 669, 1976; "Cancer Immunology and Immunotherapy", vol, 4, p. 95, 1978). Subsequent to this finding, Gram-positive bacteria which naturally and widely occur and which have no endotoxin have drawn much attention, and it was found that a peptide glycan obtained from a Gram-positive bacterium is effective in stimulating the immune system and increasing the body weight of infant swine ("Japanese Journal of Veterinary Science", vol. 49, p. 235, 1987).
The cell wall of a Gram-positive bacterium is a sack-like structure Constituted by a peptide glycan and a structure specific to the bacterium mainly composed of a polysaccharide or teichoic acid, which latter structure is covalently bonded to the peptide glycan. The cell wall contacts the outer surface of the cell membrane. The cell wall serves not only to retain the shape of the cell but also to protect the cell from various exogenous stimuli. In particular, the peptide glycan moiety is important not only for stimulating the immune system but also for retaining the shape of the cell. That is, the peptide glycan forms a large and extremely rigid polymer which constitutes a three-dimensional reticulose structure in which the glycan chain composed of N-acetylglucosamine and N-acetylmuramic acid, and the peptide chain, are bonded.
The cell walls are hitherto separated and extracted from bacteria by first removing the cytoplasmic components under specific conditions, recovering the crude cell walls remaining as a residue, and then treating the residue with a protease and a nuclease.
However, this conventional process is complicated and the yield is low. Therefore, cell walls prepared by the conventional process are too expensive as an additive in feed for domestic animals and poultry.